1. Field of the Invention
This invention relates to hydraulic lifter systems in general and more particularly to a hydraulic lifter system installed in a variable cylinder engine for reducing fuel consumption by means of controlling the number of cylinders which operates in response to the engine load.
2. Description of the Prior Art
In the prior internal combustion engine, a predetermined valve clearance is provided since there is a difference between thermal expansions of a cylinder head and a cylinder block and thermal expansions of a valve train mechanism. When the valve clearance is not properly maintained during the operation of the engine, noises will be occurred and the loss of the horse power will be occurred due to the blows of the crude gases. Therefore, the hydraulic lifters have been proposed to thereby maintain the valve clearance.
Such hydraulic lifters have a body, a plunger slidably disposed within the body so as to thereby define a reservoir chamber and a pressure chamber therein, and a check valve to allow a fluid flow only into the pressure chamber from the reservior chamber. The plunger is mechanically associated with a cam shaft and therefore the plunger is caused to be moved relative to the position of the body in response to the rotation of the cam shaft. More particularly, when the plunger is sunk relative to the position of the body, the fluid under pressure within the pressure chamber is flowed out while when the plunger is extended relative to the position of the body, the check valve is caused to be opened to thereby allow the fluid flow into the pressure chamber from the reservoir chamber.
The above hydraulic lifters have been applied in the combustion engine of variable cylinder type such that the number of cylinders, which operates, is controlled by means of the hydraulic lifters. More particularly, the check ball is pressed so as to constantly establish the fluid communication between the reservoir chamber and the pressure chamber. Therefore, the fluid pressure within the pressure chamber will be decreased and the rigidity of the hydraulic lifter will be removed so that the operation thereof becomes unavailable. The opening and closing operation of the intake or exhaust valve which corresponds to the unavailable hydraulic lifter is thus stopped.
In the valve train mechanism of pivot type wherein an upper end surface of a rocker arm is in contact with a cam surface, a lower end surface of the rocker arm is in contact with a valve stem and a coupling portion between the rocker arm and the hydraulic lifter acts as fulcrum, however, the rocker arm still carries out the rocking motion around the contact point with the valve stem even when the rigidity of the hydraulic lifter. The stroke of the hydraulic lifter becomes larger due to an arm ratio of the rocker arm and, as a result, the flow of the fluid will not follow the operation of the hydraulic lifter, and the intake or exhaust valve is still opened and closed due to the flow resistance of the fluid. Furthermore, there is a possibility that the interference between the rocker arm and the cam shaft generates the tapping noises.